Sound wave are a type of mechanical wave with behavior similar to other waves. Since sound (acoustical) waves are a longitudinal wave, they vibrate the medium parallel to the direction of propagation. This lesson will cover several basic aspects of sound waves. Allow one to two seconds for the music accompanying this slide to start. Clicking on the slide will stop the music. Clicking a second time will advance the slide.
One of the difficulties students may have is the visualization of acoustical waves since they cannot be readily seen. Challenge them to attempt to model the waves by drawing. Several of the animations in this and subsequent lessons should assist them in understanding the form of sound waves, as will visualizations on the Internet. You may find that many students draw the wave as a modification of the transverse type water wave. This is fine as long as they understand the important difference between the actual sound wave and the commonly used transverse water wave.
This animation takes a moment to load. The idea is that sound begins at the source, and is then detected by the receiver/detector. Clicking once plays a recording of a scream, with the letters of the animation moving off with the propagating waves of the scream. Clicking a second time advances the slide.
Sound is a longitudinal wave composed of regions of medium compression (called compressions) and regions of medium expansion (called rarefactions) between these. The term rarefaction comes from an old term for low pressure or near vacuum gases where the particles are far apart. These were called rarefied gases. Instill upon the students that both the compressions and rarefactions are the result of energy. It is the energy the makes possible the applied force to move the particles closer together or to move them further apart. They should be able to tell that the particles are not themselves moving across the screen in the animation, but are only vibrating back and forth. Between the time at which the medium is compressed and the medium is expanded, the medium is at rest in its normal state. This is analogous to the water in the earlier lesson being smooth, not up or down.
Because sound is a mechanical wave, it requires a medium. The first video demonstrates why this is true. The second video reinforces the required medium concept. Video three shows how the mass of the medium particles affects the propagation of the wave.
The phase of the medium affects the speed of propagation. Unlike mechanical transverse waves, sound can pass through all phases of matter including the plasma of the sun. The sun resonates on a five minute pulse acoustical wave detectable by Doppler radar. Depending upon the rigidity of the bonds and the mass of the particles, sound will propagate faster through rigid materials and slower through loosely bound materials. For example, the animation demonstrates the difference between air (gaseous), water (liquid), and ice (solid) phases. You may wish to replay this race animation by using the up arrow or the mouse wheel. Have students hypothesize where an even denser material like steel would place in the race. This type of thinking takes place in the following “Think” slide.
Because the material of the desk and your skull are more rigid, the sound should propagate through it faster – yielding a higher frequency.
This is an excellent opportunity for the students to do library or Internet research. The chart on side nine of lesson 10 would be a good starting point to show the range of sound detection (although it deals mostly with ultrasound).
Click on the Google icon to go to the search engine tutorial. After the last slide of the tutorial, you will be brought back to this slide.
<ul><li>How would you draw something you cannot see? </li></ul>Try drawing a sound wave.
Sound is a wave with recognizable characteristics. Sound waves can pass through solids, liquids, and gases.
<ul><li>Sound waves are a type of mechanical wave – </li></ul>Sound is a longitudinal wave Rarefactions are regions in which the medium particles expand farther apart. In between the compressions and the rarefactions, You can think of the compressions like crests, Sound waves are a type of mechanical wave – a longitudinal wave. In between the compressions and the rarefactions, the medium exists in its normal (at rest) state. You can think of the compressions like crests, and the rarefactions like troughs. These waves consist of a series of compressions and rarefactions. Compressions are regions in which the medium particles are pushed together.
<ul><li>Sound, as a mechanical wave, must have a medium through which to propagate. </li></ul>Not only does the medium enable the propagation of the wave, The energy that produces the force to set the medium in motion can vibrate massive particles much less than it can vibrate particles with smaller masses. Not only does the medium enable the propagation of the wave, it also affects the characteristics of the wave. Take different gas molecules for example.
The medium affects sound waves Since materials consist of particles, the type of connections between the medium’s particles can also affect how sound waves propagate. Since materials consist of particles, You may remember that longitudinal waves can pass through solids, You may remember that longitudinal waves can pass through solids, liquids, You may remember that longitudinal waves can pass through solids, liquids, gases, You may remember that longitudinal waves can pass through solids, liquids, gases, and even plasma. The closer or the more stiffly connected the particles of the medium, It is for this reason that sound travels faster through water (L) than air (G), and even faster through ice (S) than water. The closer or the more stiffly connected the particles of the medium, the faster the sound wave propagates through it. If the sound travels at different speeds, The same sound will seem different to creatures listening through the ground, the water, and the air. If the sound travels at different speeds, the pitch must change with the medium. Not only would it sound different, each type of creature has its own way of picking up those waves. It is for this reason that sound travels faster through water (L) than air (G), ice water air
During class, you place your head down on the desk with your ear against the surface. Would you expect the sounds of your teacher reprimanding you to sound higher pitched or lower pitched?
<ul><li>Reading: </li></ul><ul><li>Activity: </li></ul><ul><ul><li>Name that Tune </li></ul></ul><ul><ul><li>Sound Off </li></ul></ul>
Stretching to the Limit @ Home Animals from elephants to insects are known to use infrasound (below human hearing) for communication, and seismic waves for early warning of earthquakes. Do you think it possible for people to learn to be forewarned of earthquakes by cues from these animals?
<ul><li>Sound wave compressions are like , while rarefactors are like . </li></ul><ul><li>2. Name two animals with weird ears. </li></ul>
Review for investigating on the Internet. web links
1. Sound wave compressions are like crests , while rarefactions are like troughs .
<ul><li>2. There are lots of animals with weird ears. Crickets have ear drums on the surface of their legs. Moths have eardrums on their wings. Frogs have ear drums located behind each eye. </li></ul>